Simulated monolithic predecorated wall construction

ABSTRACT

A predecorated wallboard for forming simulated monolithic predecorated wall construction is composed of an elongated rectangular core panel including a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer and having on its front side a flat central surface arranged between recessed marginal surfaces extending from the flat surface to the opposite longitudinal edges of the panel and tapering edgewise toward the rear side of the panel, and a decorative sheet including a cloth backing layer laminated only to the flat surface of the paper facing layer on the front side of the panel throughout the length of such front side and an outer polyvinyl chloride layer forming a decorative front wall surface, such sheet also including a narrower flap extending over one of the marginal surfaces but terminating flush with the adjacent longitudinal edge of the panel and a wider flap extending over the opposite marginal surface beyond the opposite longitudinal edge of the panel. Each wallboard is adapted to form a joint with an adjacent wallboard, such as a flat joint wherein the adjacent longitudinal edges of the panels are arranged in abutting relationship and the front sides thereof are flush, with the adjacent marginal surfaces thereof forming beneath adjacent narrower and wider flaps a shallow V-shaped recess or space to be filled to the level of the flat surfaces of the panels with a hardened joint cement layer to which the narrower and wider flaps are adhered as well as to each other in overlapping relationship over the marginal surface underlying the narrower flap, the joint being completed by cutting through the overlapping portions of both flaps, by removing the overlapping and overlapped marginal edge portions of the overlying and underlying flaps respectively to cause the narrow flap to terminate short of the adjacent longitudinal edge of the underlying panel, and by readhering the remainder of the overlying flap to cause the wider flap to extend into edge abutting and flush relationship with the narrower flap to form a practically invisible seam.

United States Patent Jan. 9, 1973 211 Appl. No.: 592,356

A 52] U.s.c|. ........52/416,52/287,52/447, r 52 540,161/43 [51 'Int.- Cl ..E04b 2/10, 1332b 1/02 [58]' Field or Search ..'..'.52/416-418, 540,

894,067 11/1959 GreatBritain ..16l/44 Primary Examiner-Frank L. Abbott Assistant Examiner-James, L. Ridgill, Jr. Attorney-Sommet, Weber & Gastel ABSTRACT A predecorated wallboard for forming simulated monolithic predecorated wall construction is composed of an elongated rectangular core panel including a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paperfacing layer and having on its front side a flat central surface.

arranged between recessed marginal surfaces extending from the flat surface to the opposite longitudinal edges of the panel and tapering edgewise toward the rear side of the panel, and a decorative sheet including a cloth backing layer laminated only to the flat surface of the paper facing layer on the front side of the panel throughout the length of such front side and an outer polyvinyl chloride layer forming a decorative front wall surface, such sheet also including a narrower flap extending over one of the marginal surfaces but terininating flush with the adjacent longitudinal edge of the panel and a wider flap extending over the opposite marginal surface beyond the opposite longitudinal edge of the panel. Each wallboard is adapted to form a joint with an adjacent wallboard, such as a flat joint wherein the adjacent longitudinal edges of the panels are arranged in abutting relationship and the front sides thereof are flush, with the adjacent marginal'surfaces thereof forming beneath ad acent narrower and wider flaps a shallow V-shaped recess or space to be filled to the level of the flatsurfaces of the panels with a hardened joint'cement layer to which the narrower and wider flaps are adhered as well as to each other in overlapping relationship over the marginal surface underlying the narrower flap, the joint being completed by cutting through the overlapping portions of both flaps, by removing the overlapping and overlapped marginal edge portions of the overlying and underlying flaps respectively to cause the narrow flapto terminate short of the adjacent longitudinal edge of the underlying panel, and by readhering the remainder of the overlying flap to cause the ,wider flap to extend into edge abutting and flush relationship with the narrower flap to form a practically invisible seam.

i 6 Claims, 13 Drawing Figures PATENTEDJAH 9 I975 3.708 935 SHEET 1 OF 3 INVENTORS Donald A. Kossu'rh John D. Shull ATTORNEYS PATENTEDJAN 9191s 3 708 935 SHEET 3 [IF 3 1 SIMULATED M ONOLITI-IIC PREDECGRATED I WALL CONSTRUCTION This invention relates to simulated monolithic ing wallboards, such as gypsum boards, the two most common techniques are as follows. In one technique, individual wallboard panels are first installed over the underlying wall structure, si1ch as studs. This is followed by treating the joints with joint cement to produce a continuous surface, and then application of the'decorative coating, such'as vinyl plastic sheets, in

substantially the same manner as wallpaper, thereby requiring formation of additional joints or seams between-the plastic sheets.This technique is both time consuming and expensive because of the various separate operations required. j I v I The other technique involves installation of predecorated wallboards, followed by covering of the joints with prefabricated strips or battens either of contrasting' decorative appearance or predecorated to simulate the predecorated surface of thewallboards. Whilet his technique .'represents an improvement over the first technique from a time andexpense standpoint, it suffers in that the finished wall surfaces are far from monolithic in appearance. I

Accordingly, a primary object of the present inven- -tionis .to utilize the best features of these two prior techniques, while eliminating their disadvantages, to produce simulated monolithic predecorated wall construction having a true monolithic appearance. To this end, the present invention employs new and improved predecorated wallboards in a new and improved manner to produce new and improved joints having practically invisible seams along the wallboards in just one joint treatment operation, I for the desired monolithic appearance of the finished wall surface. As. a consequence, the present invention eliminates the separate operations of installation of undecorated wallboards followed by decoration thereof, and combines the separate wallboard and decorative coating joint treatments, all as requir'edby the first technique, while eliminating the separateinstallation of. the joint covering strips or battens of the second technique, as well as their disruptive effect on the desired monolithic appearance. Y 1

. Another object of the present invention is to provide such new and ,improved predecorated wallboards which are so constructed and designed as to form with adjacent so predecorated wallboards new and, improved jointshaving practically invisible seams. Another object is toprovide such new and improved predecorated wallboards whiehare soconstructed and designed as to permit installation thereof directly over metal studs in compliance with the American Standa'rds Association requirement of mechanical fasteners along the joints-between adjacent wallboards, while permitting theformationof newand improved finished joints which'hide the heads of such fasteners.

A furtherobject is to provide such new and improved joints having practically invisible seams by incorpor'at-v ing such new and improved predecorated wallboards and a hardened joint cement layer.

'Still another object is to provide new and improved methods of forming such new and improved joints by locating such new and improved'predecorated wallboards and treating the joints therebetween in such a manner as to produce such practically invisible seams.

Additional objects and advantages of the present invention will become apparent upon consideration of the following detailed description and accompanying drawings, wherein:

FIG. I is a fragmentary perspective view of a predecorated wallboard embodying the invention;

monolithic predecorated wall construction incorporating such wallboard and illustrating flat, inside corner and outside corner joints prior to joint treatment;

FIG. 3 is a greatly enlarged fragmentary section taken on line 3-3 of FIG. 1 and illustrating the wallboard as produced; I

- FIG. 4 is an enlarged fragmentary horizontal section taken through the encircled portionof the flat joint shown in FIG. 2;

FIGS. 5' and 6 are views similar to FIG. 4, but taken during and following the joint treatment operation, respectively; i

FIG. 7 is an enlarged, fragmentary horizontal section taken through the encircled portion of the outside corner joint shown in FIG. 2; r

FIGS. 8 and 9 are views similar to FIG. 7, but taken during and following the joint treatment operation, respectively; l FIG. 10 is an enlarged, fragmentary horizontal section taken through the encircled portion of the inside comer-joint shown in FIG. 2; 1

FIGS. 11 and 12 are views similar to FIG. .10, but taken during and following the jointtreatment operation, respectively, and I FIG. 13 isan enlarged, fragmentary horizontal section taken through the encircled portion of FIG. 2, and illustrates a joint between a wallboard and an underly-. ing stud intermediate the wallboard edges.

Referring to the drawings, and particularly FIGS. 1 and 3,' a predecorated wallboard constituting a preferred embodiment of the invention is indicated generally at 10. This wallboard preferably includes a core panel 12 of elongated, generally rectangular gin'al surfaces 18 which preferably taper edgewise towardrear surface 20, and which extend froinsurface 16 to opposite longitudinal edges 22 of the core panel. Decorative sheet 14 is laminated only to'flat surface 16 by suitable adhesive layer 24 during manufacture'of wallboard l0, and includes a shorter flap 26jextending over one of marginal surfaces 18 at least adjacent, and

preferably terminating substantially flush vvwitln] one 1 edge 22 of core panel 12. Sheet 14 also includes a longer flap 28 which extends over the oppositemarginal surface 18 at least beyond the opposite edge 22 of such opposite longitudinal edge onto the rear side 20 of FIG. 2 is a fragmentary perspective view of simulated v secured to such rear side 20 by suitable means such as adhesive bead-30 duringmanufacture of the wallboard,

and which beadpreferably is coextensive 'withlthe length of panel l2.v I v r From a constituent standpoint, wallboard 10 has the following preferred construction. The adhesive layer 24 laminating decorative sheet to flat surface 16 and a adhesive bead 30 are of a dextrine type, e.g. a borated dextrine. Core panel 12 is composed of a set cementitious, and preferably gypsum, core 32 enclosedon its two opposite sides and two longitudinal edges with a fibrous, and preferably paper, facing layer 34. Decorm tive sheet 14 includesan inner fibrous, and preferably cloth, backing layer 36, which is laminated to the paper facing layer 34; forming flat surface 16, and an outer plasticjand preferably polyvinyl chloride, layer 38- forming a decorative front wall surface. The fibrous backing layer 36 is provided to give dimensional stability to the outer plastic layer 38 during manufactureof composite sheet l4, during laminationof such sheet to core panel'lz, and during'cutting of flaps'26, 28'when forming joints. Pla'stic layer 38 may be embossed, printed or otherwise decorated to provide the desired decorative outer or front wall surface.

From a dimensional standpoint, wallboard 1 has the. following preferred construction. The overallnominal 4 inches and longer:flap'28..with a width of about A inches. The: fibrous backing layer 36 of, decorative sheet 14 isabout three vtimes theuthickness of plastic layer 38, typical thickness dimensions beingl2lmils ancl4'mils respectively, The typical widthof each mar? ginal surface -18 is about 2 a inches, which ordinarily leaves about 1 inches at each marginal portion of flat surface .l6 unadhered to overlying sheet 14. This is for facilitating the joint treatment operation to vbe described below, by permitting the flaps on adjacent panels tobe folded or peeled back and away from the joint betweenltwo adjacent core panels, for free'and unemcumbe r'ed entry of a broad knife in applying joint cement and for applyingadhesive to the underside of the flaps. However, the extent-of such unadhered area between flat surface 16 and sheet 14 is not critical.

Typically; each tapering marginal surface l8 has a widthof, about 2 a. inches and a depth of about 0.06

for facilitating the, joint treatment is about'42/l while thexminiinumpermissibleratioisabout 3.75/1. M

' This; substantially greater" width .then depth "characteristic of each tapering marginal surface 18 is animportant feature of the invention for providingp-an adequate surface. through whichfastener's' may be driven .adjacent' the joint between two adjacent wall-I boards 10, particularly inv installing suchwallboards directly over metal studs, {because it is required by the American Standards Association that when wallboards areso installed, they must be mechanically fastened along such joints. A typical predecorated wallb'oard now in commercial use is providedwith a cha'mfered longitudinal edge of about three-sixteenths inch in both width and depth. This does not provide a sufficient bearing surface for the heads of fasteners to be driven into such metal studs at such joints. Accordingly, when using such typical .chamfered predecorated wallboard's, a double wall construction must be used to comply with this A.S.A. requirement.

In contrast, the inventive predecorated wallboard 10, by i'easo'n of marginalsurfaces l8 pro'viding a recessed, and preferably tapering, width to depth ratio of at least 3.7511 with a minimum width of about 0.75 inch, presents an adequate bearing surface for the fastener heads'in compliance with such A.S.A. standard, and eliminates the need for such double wall construction. This is theonly predecorated wallboard known to us to satisfy such standard, while permitting joint treatment to hide "such fastener heads and produce practically invisible seams for the desired monolithic wall surface appearance. I f v [While the inventive'wallboard 10 obviouslymay be applied over existing wall surfacesor any other suitable skeletel supporting wallstructure, such as thetypical wooden studs, it is especially useful, as noted above, for direct application" to metal studs, such as thoseyin dicated generally at 40 in the drawings'Referring' particularly 'to' FIG. 2, a typical simulatedmonolithic preclecorated wall construction incorporating such wallboards 10 isshown as includingflrom left to right, a

flat joint, an inside corner joint'andan outside corner joint. At each joint,-such as illustrated in greater detail v each core panel12.

in order to maintainja substantially continuous decorativesurface along the joints formed between such studs 40 and the wallboards intermediate the lon-' gitudinal edges of such wallboards, the, rear surfaces 20 of such wallboards are secured to such studs 40 by 1 means of adhesive layer ,as shown in greater detail in FIG. 13.This adhesive layer maybe of any suitable type which'is' compatible with'and adheres fto the materials of the wallboard and the underlying supporting wall structure, e.g. paper and metalfPreferably, layer 44 is of the "modified contact type adhesive, which'has sufficient strength on contact to support wallb'oa rds l0 in'the desired position, but does not take apermanent set for an extended period of time, so as to permit adjustment of the positions of such wallboa'rcls, ifnecessary; v I I lnpracticing the-inventivemethod of forming various joints in simulated monolithic;predecoratedwall construction, such as shown in FIG.L2, it ispreferred that the various wallboards lofirstbe installed over studs), followed bytreating and finishing the various joints, 'e.g. by moving clockwise inFlG. 2. Generally speaking, for each of the illustrated and other. joints, the corresponding wallboards are arranged adjacent each other by locating their corepanels 12 so that one panel has one longitudinal edge substantially abutting the adjacent longitudinal edge or side of the other panel and one side substantially flush with the adjacent side or edge of the other panel; byfilling the space between one flap, namely flap 26, and the underlying marginal surface with joint cement extending beyond such flap to substantially the level of flat surface 16 and allowing the joint cement to form a hardened layer; by adhering both flaps, such as 26 and 28, to the hardened cement layer and each other, with the flaps overlapping over marginal surface 18 underlying such one flap 26, by cutting through the overlapping portions of both flaps over the hardened cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap to cause such one flap 26 to terminate short of its panel's longitudinal edge 22 over the underlying marginal surface 18, and by readhering the remainder of the overlying flap to cause the other flap, such as 28, to extend over the exposed surface of the hardened cement layer into substantially edge abutting and flush relationship with the one flap 26, to form a practically invisible longitudinal seam along the joint.

After forming either a flat joint,-an outside corner joint, or an inside corner joint, such as those shown in the drawings, additional joints readily may be formed on either or both sides of the originally formed joint, inasmuch as each wallboard it) originally includes a longer flap, such as 28 and a shorter flap, such as 26. Hence, prior to or following formation of a particular joint, such'as the flat joint shownin FIGS. 4-6, wherein longer flap 28 on the left hand panel 12 and shorter flap 26 on the right hand panel 12 have been arranged'in the desired substantially abutting and flush relationship, the left hand core panel 12 still has a shorter flap 26 (FIG. 3) which is adapted to be arranged in the peating the aforesaid locating, filling, adhering, cutting and readhering steps, additional joints are likewise formed with practically invisible longitudinal seams.

Referring now to FIGS. 4-6 in particular, the desired substantially flat joint is formed by locating and fastening adjacent panels 12 on stud 40 by screws 42 so that one panel has one longitudinal edge 22 arranged in substantially abutting relationship with the adjacent longitudinally edge of the other panel and its front side substantially flush with the front side of the other panel, with-the adjacent recessed marginal surfaces 18 tapering edgewise toward each other and rear'surfaces 20. Previously, as in forming each joint, flap 28 is removed from rear surface 20 (FIG. 3), and both adjacent flaps 26, 28 arefolded back out of the way to expose the unadhered marginal portions of flat surfaces 16 as well as recessed marginalsurfaces l8, somewhatas shown in FIG. 4, and actually secured temporarily to sheet 14, preferably by masking tape (not shown), to facilitate the joint treatment operation. The space between each quick setting type of cement be used, rather than a slow drying type, in order to speed the joint treatment and finishing operation. A typical joint cement of the quick setting type, which has been found to be particularly useful in practicing the present invention, is described in Canadian Pat. No. 715,620.

After cement layer 46 has sufficiently hardened, flaps 26, 28 are unfolded and adhered to the exposed surface of such layer, the marginal portions of surfaces 16 and to each other in any suitable manner, but preferably by applying suitable adhesive paste at least to the undersides of the flaps. One suitable adhesive paste which has been found to be particularly useful in practicing the invention, is wheat paste. Flaps 26, 28 are adhered, as noted above, with such flaps overlapping over marginal surface 18 underlying flap 26. As shown in FIG. 5, flap 28 overlaps flap 26, although the latter could overlap the former.

The next step involves cutting through the overlapping portions of both flaps 26, 28, such as along line L, shown in FIG. 5, by'means of any suitable cutting instrument. Next the overlapping marginal edge portions, such as'28a, of overlying flap 28, and the overlapped marginaledge portion, such as 26a, of underlying flap 26, are removed, thereby causing flap 26 to terminate v short of the adjacent longitudinal edge 22 of righthand core panel 12. Preferably, after removing marginal edge portion 28a, flap 28 is peeled or folded back to facilitate stripping of marginal portion 26a.

Following such removal, the remaining portion of flap 28 is readhered to the underlying marginal portion of left surface 16 and layer 46, such as shown in FIG. 6,

' necessary, any adhesive paste which may have been marginal surface 18 and each flap 26, 28 is filled with removed by striping marginal portion 28a or 26a may be reapplied prior to readhering flap 28 or 26,-and any excess paste may be wiped off. I

Application of the inventive method to formation of a typical outside corner joint, such as shown in FIGS. 7-9, involves the same sequence of steps, but with the following differences. As so often happens when coming to a corner, the wallboard is too long, and this is the situation shown in FIGS. 7-9. Hence, prior to fastening the vertically illustrated wall panel 10 to the underlying studs 40, it is necessary to cut such wallboard to the appropriate length. This often involves, as shown in FIG. 7, cutting back core panel 12 and stripping a flap, such as 28, back from the underlying core panel 12 to such an extent that no recessed marginal surface 18 is left.

Thus, former edge 22 is converted into newly formed longitudinal edge 50, and flap 28 is converted to stripped back flap 52. I

I Nevertheless, in forming such an outside comer joint, the method involves basically the same locating step as in FIGS. 4-6, except that the two core panels 12 are locatedso that one panel, such as vertical panel 12 in FIGS. 7-9 has one longitudinal edge, such as 50, arranged insubstantially abutting relationship with the rear side of horizontal panel 12, and its front side sub- 7 stantially flush'with the adjacent longitudinal edge 22 of horizontal panel 12, to form an angle of more than 180 between such front sides, about270 being" shown. At the same time,'one panel, such as horizontal panel 12, has on its front side a recessed tapering marginal surface 18 extending from flat'surface 16 to longitudinal edge 22 adjacent vertical panel 12, with sheet 14 on horizontalpanel 12 having-flap 26 terminating sub- .tion, toform the preferred sharp corner, as opposed to the substantially isosceles triangular cross section of layer 46 in FIGS; 4 --6. Flaps 52 and 26 are adhered to the underlying surfaceof cement layer 54 and to each other, as before, except that flap 52. is first extended over edge 22 'of horizontal panel 12 and turned over layer 54 to form the underlying flap, while flap 26 forms the overlying flap, as shown in FIGJ8. The purpose of reversing the relative positions of such flaps, as compared to that shown in FIGS. 4-6, is to avoid,'as much as possible, disturbing the desired, preferably sharp corner shape of cement layer 54. After cutting through both flapsalong a'linesuch as L,, marginal portions 26a and 52a are removed, whereupon the readhered remaining portion of flap 26. 'extendsinto substantially abutting and flush relationship with the remaining adhered portion of. flap 52, to form the desired, practically invisible longitudinal seam.

' Referring to FIGS. -12, a typical insidecorner joint is shown therein, wherein itwas found to be necessary to cut down the length of wallboard 10 form- .sides of the panels, 90 being shown. At the same time,

one panel, such as vertical panel 12, has a recessed marginal surface 18, while sheet 14 on such vertical panel has a flap, such as26, of such a length as to terminate substantially flush with edge 22, while flap 58 is long enough to extend beyond edge 56.

The space between marginal surface 18 and flap 26 is 7 filled with joint cement which extends to the front side of horizontal panel.12, which is beyond flap 26 after being cut, as shown in FIG. 12, to substantially the level of flat surface 16 on vertical. panel 12. Once again, upon hardening, the resulting cement layer 60 is of generally right triangular cross section to form the ing the right half portion of the flat joint shown in FIG'S.- I

4'6,Iin,order to form the desired inside comer. joint, v

just as it was found necessary to cut down the length of the wallboard 10 forming the left hand or upper portion or the outside corner joint shown in FIGS.- 7 9.-To this end, it was necessary to strip longer'flap'28 of the upper or horizontal wallboard l0 inFIG. 10 back along flat surface 16, andto entirely remove marginal surface 18, inorder to form a new longitudinaledge 56' on such horizontal wallboard. Thus, flap 28 is necessarily converted to flap 58in FIG. 10. a

After such stripping and edge forming operation, the

panels are located and fastened to studs 40 a in the manner shown, it being noted that the head of screw 42.

as horizontal panel 12 in FIG. 10,'has one longitudinal edge, such as 56, ar1'anged in substantially abutting relationship with the front side of the other panel, such as vertical panel 12,. and its rear side substantially flush with the adjacent longitudinal edge 22 of vertical panel 12, to form an angle'of lessthan 180 between the front desired sharp inside 'corner, and flap 58 is first turned over the exposed surface of layer 60 to form the underlying flap to avoid disturbing such corner.

' Following the adhering step, the overlapping flap portions are out along line L,, whereupon marginal portions 26a and 58a are removed, with the remaining portion of flap 26 being readhered to extend into the desired substantially abutting andv flush relationship It now will be seen howjthe invention accomplishes its various objects,'and the numerous advantages of the invention likewise will be apparent. While'the invention has been described and illustrated herein by reference to certain embodiments, it is to be understood that variouschanges-and modifications may be made therein by those skilled in the art, without departing from the inventive concept, the scope of which is to be determined by the appended claims.

What is claimed is: V a

1. A predecoratedwallboard for forming joints having practically invisible seams in simulated monolithic predecorated wall construction and comprising a core panel of elongated generally rectangular shape and having ;on its front side a substantially flat central surface having opposite marginal portions and arranged between recessed marginal surfaces extending from said opposite marginal portions of saidflat central surface to opposite longitudinal edges of said core panel, said recessed marginal surfaces having a substantially greater width than depth with a minimum width of about 0.75 inch, and a:decorative sheet forming a decorative plastic front wall surface, said sheet being laminatedonly to said flatcentral surface, but not to said marginal portions thereof nor to. said recessed marginal-surfaces,throughout the length of said front side and including one flap extending over one of said marginal portions and one of said recessed marginalsurfaces adjacent thereto and terminatingsubstantially flush with one longitudinal edgeof said core panel and another flap extending over the opposite marginal portion and the opposite recessed marginal surface adjacent thereto around the opposite longitudinal edge onto the'rear side of said core panel and being temporarily secured to butremovable from said rear side to overlap with an adjacent flap corresponding to said one taper edgewise toward the rear side of said core panel and have a minimum width todepth ratio of about 3.75/1, and said decorative sheet includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface.

3. In Simulated monolithic predecorated wall construction, a substantially flat joint including two adjacent predecorated wall boards, each comprising a core panel having on its front side a substantially flat surface having a marginal portion and a recessed marginal surface extending from said marginal portion of said flat surface to an edge, said recessed marginal surface having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only to said flat surface, but not to said marginal portion nor to said recessed marginal surface, one of said decorative sheets on one of said core panels including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto at least adjacent one of said edges prior to completion of said joint, the other of has on its front side a substantially flat central surface said decorative sheets on the other of said core panels including another flap extending over the other of said marginal portions and the other of said recessed marginal surfaces adjacentthereto at least beyond the other of said edges to overlap with said one flap prior to completion of said joint, said core panels beingarranged with saidfront sides substantially flush, said recessed marginal surfaces adjacent, said edges in substantially abutting relationship and said flaps adjacent, a hardened joint cement layer filling the space between said recessed marginal surfaces and flaps to substantially the level of said flat surfaces, and upon completion of said joint, said flaps being adhered to and extending over said marginal portions and said cement layer into substantially edge abutting and flush relationship to form a'practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said flaps to said marginal portions, cement layer and each other with said, flaps overlapping, cutting through the overlapping portions of said flaps over said cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlyingxflap to the underlying one of said marginal portions and said cement layer. v I

4. The joint of claim 3 wherein each of said core panels includes aset cementitious core enclosed on opposite sides and each of said abutting edges with a fibrous facing layer, said marginal surfaces taper edgewise toward'the rear sides of said core panels and have a minimumwidth'to depth ratio of about 3.75/1,

' and each of said decorative sheetsincludes an inner fibrous backing layer laminated to said fibrous facing layer and an outer plastic layer forming a decorative front wall surface.

5. The joint of claim 3 wherein each of said core having opposite marginal portions and arranged between recessed ,marginal surfaces extending from said opposite marginal portions of said flat central surface to opposite edges of said core panel, said recessed marginal surfaces having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only tosaid flat central surface, ,but not to said marginal portions thereof nor to said recessed marginal surfaces, throughout the length of said front'side and including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto and terminating substantially flush with one longitudinal edge of said core panel prior to completion of said joint and another flap extending over the opposite marginal portion and the opposite recessed marginal surface adjacent thereto at least beyond the opposite longitudinal edge of said core panel to overlap with an adjacent flap corresponding to said one flap prior to completion of said joint, said core panels being arranged with said front sides substantially flush, said one recessed marginal surface on one of said core panels adjacent said opposite recessed marginal surface on the other of said core panels, said one longitudinal edge of said one core panel in substantially abuttingrelationship with said opposite longitudinal edge of said other corepanel and said one flap on said one core panel adjacent said other flap on said other core panel, a hardened joint cement layer filling the space between said adjacent recessed marginal surfaces and flaps to substantially the level of said flat central surfaces, and upon completion of said joint, said one adjacent flap being adhered to and extending over said one marginal portion and said cement layer but terminating short of said one abutting edge and said other adjacent flap being adhered to and ex tending over said opposite marginal portion and said cement layer beyond said other abutting edge into substantially edge abutting and flush relationship with said one adjacent flap to form a practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said adjacent flaps to said marginal portions, cement layer and each otherwith said adjacent flaps overlapping, cutting through the overlapping portions of said adjacent flaps overjsaid cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlying flap to the underlying one of said marginal portions and said cement layer.

6. The joint of claim 5 wherein each of said core panels includes a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer, said recessed marginal surfaces taper edgewise toward'the rear sides of said core panels and have a minimum width to depth ratio of about'3.75/l, and each of said decorative sheets includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface.

I e .1: =0: is =0: 1 

2. The predecorated wallboard of claim 1 wherein said core panel includes a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer, said recessed marginal surfaces taper edgewise toward the rear side of said core panel and have a minimum width to depth ratio of about 3.75/1, and said decorative sheet includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface.
 3. In simulated monolithic predecorated wall construction, a substantially flat joint including two adjacent predecorated wall boards, each comprising a core panel having on its front side a substantially flat surface having a marginal portion and a recessed marginal surface extending from said marginal portion of said flat surface to an edge, said recessed marginal surface having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only to said flat surface, but not to said marginal portion nor to said recessed marginal surface, one of said decorative sheets on one of said core panels including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto at least adjacent one of said edges prior to completion of said joint, the other of said decorative sheets on the other of said core panels including another flap extending over the other of said marginal portions and the other of said recessed marginal surfaces adjacent thereto at least beyond the other of said edges to overlap with said one flap prior to completion of said joint, said core panels being arranged with said front sides substantially flush, said reCessed marginal surfaces adjacent, said edges in substantially abutting relationship and said flaps adjacent, a hardened joint cement layer filling the space between said recessed marginal surfaces and flaps to substantially the level of said flat surfaces, and upon completion of said joint, said flaps being adhered to and extending over said marginal portions and said cement layer into substantially edge abutting and flush relationship to form a practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said flaps to said marginal portions, cement layer and each other with said flaps overlapping, cutting through the overlapping portions of said flaps over said cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlying flap to the underlying one of said marginal portions and said cement layer.
 4. The joint of claim 3 wherein each of said core panels includes a set cementitious core enclosed on opposite sides and each of said abutting edges with a fibrous facing layer, said marginal surfaces taper edgewise toward the rear sides of said core panels and have a minimum width to depth ratio of about 3.75/1, and each of said decorative sheets includes an inner fibrous backing layer laminated to said fibrous facing layer and an outer plastic layer forming a decorative front wall surface.
 5. The joint of claim 3 wherein each of said core panels is of elongated, generally rectangular shape and has on its front side a substantially flat central surface having opposite marginal portions and arranged between recessed marginal surfaces extending from said opposite marginal portions of said flat central surface to opposite edges of said core panel, said recessed marginal surfaces having a substantially greater width than depth with a minimum width of about 0.75 inch, and a decorative sheet laminated only to said flat central surface, but not to said marginal portions thereof nor to said recessed marginal surfaces, throughout the length of said front side and including one flap extending over one of said marginal portions and one of said recessed marginal surfaces adjacent thereto and terminating substantially flush with one longitudinal edge of said core panel prior to completion of said joint and another flap extending over the opposite marginal portion and the opposite recessed marginal surface adjacent thereto at least beyond the opposite longitudinal edge of said core panel to overlap with an adjacent flap corresponding to said one flap prior to completion of said joint, said core panels being arranged with said front sides substantially flush, said one recessed marginal surface on one of said core panels adjacent said opposite recessed marginal surface on the other of said core panels, said one longitudinal edge of said one core panel in substantially abutting relationship with said opposite longitudinal edge of said other core panel and said one flap on said one core panel adjacent said other flap on said other core panel, a hardened joint cement layer filling the space between said adjacent recessed marginal surfaces and flaps to substantially the level of said flat central surfaces, and upon completion of said joint, said one adjacent flap being adhered to and extending over said one marginal portion and said cement layer but terminating short of said one abutting edge and said other adjacent flap being adhered to and extending over said opposite marginal portion and said cement layer beyond said other abutting edge into substantially edge abutting and flush relationship with said one adjacent flap to form a practically invisible seam produced by folding said flaps back out of the way to expose said marginal portions and recessed marginal surfaces prior to said filling of said space with said cement layer, adhering said adjacent flaps to said marginal portions, cement layer and each other with said adjacent flaps overlapping, cutting through the overlapping portions of said adjacent flaps over said cement layer, removing the overlapping marginal edge portion of the overlying flap and the overlapped marginal edge portion of the underlying flap and readhering the remainder of the overlying flap to the underlying one of said marginal portions and said cement layer.
 6. The joint of claim 5 wherein each of said core panels includes a set gypsum core enclosed on its two opposite sides and two longitudinal edges with a paper facing layer, said recessed marginal surfaces taper edgewise toward the rear sides of said core panels and have a minimum width to depth ratio of about 3.75/1, and each of said decorative sheets includes an inner cloth backing layer laminated to said paper facing layer and an outer polyvinyl chloride layer forming a decorative front wall surface. 